1. Field of the Invention
Our invention is a unidirectional distance measuring system which operates by transmitting and receiving both radio and low frequency sound waves between two points.
2. Description of the Prior Art
Many prior art inventions use the simultaneous transmission of sound and radio waves to measure distances between points. Most, such as sonar, depend on receiving reflected sound waves back from a surface. Our invention is not concerned with these types of systems which depend on receiving reflected sound since it measures the distance in one direction only. Of the known prior art the U.S. Pats. Nos. 1,126,095 to Schiessler, 1,138,013 Phinney, 3,731,273 and Hunt appear closest to our invention. Each, however, differs in several important aspects. The Schiessler invention does not operate over land without intervisibility by sending a substantially fixed amplitude sound wave of low frequency as the measuring phenomenon. Phinney's system depends on the judgment of the operators to a large degree and employs no specific audio or radio frequencies. In Hunt's invention the triangulation method with two microphones or a spark gap is needed. Further, in the Hunt system the position of the electrical signal generator is critical to its operation. Such is not the case with our invention as the distance being measured is to a large degree completely independent of the location of the sound and radio wave source or its receiver.
Our invention was primarly developed to measure distances between two points in cases where there was a lack of intervisibility between observers located at these points. A good example of its use can be found in measuring lateral distances from the center line rights of way for high power transmission lines in the dense forests of the Pacific Northwest. In such an environment direct line of sight devices cannot be used because of the lack of intervisibility. High frequency sound waves have also proven unsuitable as they are affected to a large degree by the dense growth between observers. Using measuring tapes is also unacceptable due mainly to the time element in making the measurements. What we have invented overcomes all of these restrictions and drawbacks and yet is nonaffected by environmental conditions such as rain, fog, darkness or the like. It is also so simple to operate that even untrained non-technical personnel can achieve accurate results.